1. Field of the Invention
The present invention relates to a transmission of an internal combustion engine. More particularly, to a transmission of an internal combustion engine applied to a motorcycle.
2. Description of Background Art
Japanese Patent Laid-Open No. 2007-78086, for example, discloses a transmission for an internal combustion engine structure that includes a primary reduction gear for the transmission. More specifically, Japanese Patent Laid-Open No. 2007-78086 discloses a primary drive gear provided relative to a crankshaft wherein a primary driven gear is driven by the primary drive gear. A reduction gear bearing is provided between the primary driven gear and a clutch outer. A wall portion of a power unit case supports the reduction gear bearing. A clutch center is rotated by receiving power from the clutch outer. A main shaft rotates integrally with the clutch center.
In the structure described in Japanese Patent Laid-Open No. 2007-78086, though not disclosed in detail in the conventional example, the primary drive gear and the primary driven gear are helical gears. Thus, when the crankshaft rotates, the primary driven gear receives a thrust load to the clutch side. Because the thrust load is received, the above-described reduction gear bearing and the wall portion of the power unit case for supporting the reduction gear bearing are set in the conventional example. Therefore, the conventional example has a problem of a long shaft length of the transmission main shaft provided with the clutch.